The present invention relates to electromagnetically-actuatable actuators which have at least one electromagnet and an armature that acts on a device to be set or controlled, with the armature being connected to at least one restoring arrangement so the armature can be moved, by the switching on of the coil current of the electromagnet, from a first set position that is predetermined by the restoring arrangement into a second set position defined by the contact of the armature with the electromagnet. Electromagnetically-actuatuble actuators are used, for example, to control cylinder valves in reciprocating engines. In this instance, two electromagnets are provided, between which the armature can be moved, counter to the force of a restoring arrangement, through the cutoff of the coil current at the holding electromagnet and the switching on of the coil current at the capturing electromagnet, respectively. With corresponding actuation of the individual actuators of the individual cylinder valves, the work medium can flow in and out, so the work process can be optimally influenced with respect to the necessary considerations. The procedure of the control has a great influence on the different parameters, such as the states of the work medium in the inlet region, the work chamber, e.g., a combustion chamber, and the outlet region, as well as on the processes in the work chamber itself. Because reciprocating engines operate unsteadily, that is, under widely-varying operating conditions, a corresponding, adaptable control of the cylinder valves is necessary. Electromagnetically-actuatable setting arrangements for cylinder valves are known from, for example, DE-C-3 024 109, corresponding to U.S. Pat. No. 4,455,543 which is incorporated herein by reference, such setting arrangements permit a completely-variable adaptation of the opening and closing times.
A significant problem in controlling such electromagnetically-actuatable setting arrangements is timing precision, which is necessary particularly in the control of the engine power for the intake valves. Precise control of the times is impeded by manufacturing-stipulated tolerances, the occurrence of wear in operation, and different operating states, for example, fluctuating operating frequencies, because these external influences can also impact the time-relevant system parameters.
One approach to attaining high control precision involves the application of a comparatively high energy for capturing the armature at a respective magnet pole surface. However, this high energy expenditure is associated with a reduced operating reliability, because the further problem of so-called armature bouncing occurs to a greater extent. This problem occurs because the armature impacts the pole surface at a high speed and bounces away from it immediately or shortly thereafter. In cylinder valves, for example, this bouncing negatively influences the operation of the engine. In order to save energy, when the armature lies against the magnet pole surface, the supply of the current to electromagnet is reduced to the amount necessary to hold the armature, and the current supply is clocked between an upper and a lower level for further savings. It is also important that the armature actually be held against the magnet pole surface.
It is the object of the invention to provide a method that permits flawless recognition of whether the armature lies against the electromagnet pole surface, for example, for diagnostic purposes.